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So I'm currently working on a set of scientifically plausible star systems, and I want to make one of the moons of a planet colored in patches of medium brown and pale brown dust/rock, but I can't find anything on what minerals can form without an atmosphere, water, or anything that our moon doesn't have. I've already decided on the characteristics of the parent star and parent planet, and the formation of the moon.
The star is an M2.7V type star, and its exact surface temperature is 3,234 K. The parent planet is an Earth-like planet, with two moons, including the one I'm trying to figure out currently. The moon has a mass of about 0.02 times the mass of earth, so a bit larger than our moon.
By the way, there is an intelligent civilization on this planet, they have eyes adapted for light under a K2.7V type star. Also, I just realized the numbers for their old star and new star are the same, just with a different spectral class haha.
Not sure if this is too much detail, I don't really know if any of this would affect the color of the moon.

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  • $\begingroup$ Geology of the Moon. Note the large percentage of silica, the mineral of which most Earth sand is made. (And anyway just about any mineral can have a wide variety of colors. The idea that each mineral has a well-defined specific color is naive.) (Here is a color picture of a small part of the Moon taken by the crew of Apollo 15; it looks pretty khaki to me.) $\endgroup$
    – AlexP
    Commented Sep 28, 2022 at 15:40
  • $\begingroup$ Ja Cobber you tell `em! Send us paint! Millions and millions of cans of paint! I spray it on I betcha! $\endgroup$
    – BillOnne
    Commented Sep 28, 2022 at 16:09
  • $\begingroup$ @AlexP so basically, I can just say the color is caused by impurities in the soil? I'm imagining that the dust on the surface is similar to moon dust, in that it's made of similar minerals, simply with different impurities $\endgroup$
    – isdi0
    Commented Sep 28, 2022 at 16:15
  • $\begingroup$ Your moon could have once had an atmosphere, and Iron on the surface oxidized (like on Mars). The rust remains, even if the liquids & gasses are long gone. $\endgroup$
    – DWKraus
    Commented Sep 28, 2022 at 16:59

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Tholins, you thay?

https://en.wikipedia.org/wiki/Tholin

tholiny asteroid

Tholins (after the Greek θολός (tholós) "hazy" or "muddy";[2] from the ancient Greek word meaning "sepia ink") are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds... Tholins are disordered polymer-like materials made of repeating chains of linked subunits and complex combinations of functional groups, typically nitriles and hydrocarbons and their degraded forms such as amines and phenyls. Tholins do not form naturally on modern-day Earth, but they are found in great abundance on the surfaces of icy bodies in the outer Solar System, and as reddish aerosols in the atmospheres of outer Solar System planets and moons.

Lots of bodies on our solar system sport a brownish red tholin coat; linked wikipedia lists a bunch. Above is the Ultima Thule asteroids which has a cinnamon tholin color. Enceladus has brown tholins in its cracks. I sympathize, En!

If Mars iron red is not what you are looking for you can assert your moon has tholins. Our moon does not have much iron on its surface and no tholins I know of (too much radiation?). But for a moon tholins are another route to brown.

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